Session-by-session adjustment of a device for treating sleep disordered breathing

ABSTRACT

A method is disclosed for operating a device that treats sleep disordered breathing (SOB) during successive treatment sessions, where the device provides continuous positive airway pressure during sleep. The method comprises the steps of applying a constant treatment pressure during a first session and deriving a sleep disorder index (SOl) representative of the number of SOB episodes that occurred during the first session. If the treatment pressure should be increased based upon the derived SOl, it is increased during a second, subsequent session.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/039,548, filed Mar. 3, 2011, which is a continuation of U.S.patent application Ser. No. 10/597,291, filed Jul. 19, 2006, now U.S.Pat. No. 7,913,691, which is a National Phase of PCT/AU05/00174, filedFeb. 10, 2005, which claims the benefit of U.S. Provisional ApplicationNo. 60/543,491, filed Feb. 11, 2004, the disclosure of which isincorporated herein by reference. The invention relates to devices fortreatment of sleep disordered breathing (SOB). More specifically, theinvention relates to a device for detecting SOB events in the presenceof a continuous positive airway pressure and determining an appropriateadjustment to the airway pressure in response to detected SOB events.

BACKGROUND OF THE INVENTION

The present invention relates to the diagnosis and treatment of partialor complete upper airway occlusion, a condition in which the upperairway collapses, particularly under the reduced pressure generated byinhalation. This is most likely to happen during unconsciousness, sleepor anesthesia.

A particular application of the present invention is to the diagnosisand/or treatment of snoring and sleep apnea. Sleep apnea ischaracterized by complete occlusion of the upper airway passage duringsleep while snoring is characterized by partial occlusion. Anobstructive sleep apnea sufferer repeatedly chokes on their tongue andsoft palate throughout an entire sleep period, resulting in loweredarterial blood oxygen levels and poor quality of sleep. It should berealized that although the following specification discusses sleep apneain detail, the present invention also applies to the diagnosis andtreatment of other forms of upper airway disorders.

The application of continuous positive airway pressure (CPAP) has beenused as a means of treating the occurrence of obstructive sleep apnea.The patient is connected to a positive pressure air supply by means of amouth and nose mask, nose mask only or nasal prongs. The air supplybreathed by the patient is at all times at slightly greater thanatmospheric pressure. For example, therapeutic pressures will typicallybe within the range of 4 cmH₂O to 20 cmH₂O. It has been found that theapplication of continuous positive airway pressure (CPAP) provides whatcan be described as a “pneumatic splint”, supporting and stabilizing theupper airway and thus eliminating the occurrence of upper airwayocclusions. It is effective in eliminating both snoring and obstructivesleep apnea, and in many cases is effective in treating central andmixed apnea.

The airway pressure required for effective CPAP therapy differs frompatient to patient. In order to discover the airway pressure which ismost effective for a particular individual, the practice has been forthe patient to undergo two sleep studies at an appropriate observationfacility such as a hospital, clinic or laboratory. The first night isspent observing the patient in sleep and recording selected parameterssuch as oxygen saturation, chest wall and abdominal movement, air flow,expired CO₂, ECG, EEG, EMG and eye movement. This information can beinterpreted to diagnose the nature of the sleep disorder and confirm thepresence or absence of apnea and, where present, the frequency andduration of apneic episodes and extent and duration of associated oxygendesaturation. Apneas can be identified as obstructive, central or mixed.The second night is spent with the patient undergoing nasal CPAPtherapy. When apnea is observed, the CPAP setting is increased toprevent apneas. The pressure setting at the end of the sleep period,i.e., the maximum used, is deemed to be the appropriate setting for thatpatient.

For a given patient in a given physical condition, various stages ofsleep will require different minimum pressures to prevent occlusions.Furthermore, these various pressures will, in fact, vary from day to daydepending upon the patient's physical condition, for example, nasalcongestion, general tiredness, and effects of drugs such as alcohol, aswell as the patient's sleeping posture. Thus the appropriate pressurefound in the laboratory is necessarily the maximum of all these minimumpressures for that particular night and is not necessarily the idealpressure for all occasions nor for every night. It will generally behigher than necessary for most of the night.

Also, a patient must be able to operate a CPAP system to deliverappropriate airway pressure at home where their general physicalcondition or state of health may be quite different from that in thesleep clinic, and will certainly vary from day to day. The patient'sphysical condition often improves due to CPAP therapy. It is often thecase that after a period of therapy the necessary airway pressure can bereduced by some amount while still preventing the occurrence ofobstructive sleep apnea.

The long term effects of CPAP therapy are unknown so it is desirable tokeep the airway pressure as low as practicable, particularly if apatient requires long term treatment. Lower airway pressures also resultin a lower face mask pressure which is generally more comfortable forthe patient. It has been found that CPAP induces patients to swallow andthis inducement to swallow can be reduced by lowering the airwaypressure. Thus it is desirable to use the lowest practicable airwaypressure that is effective in preventing airway occlusion during CPAPtherapy for the comfort and possibly the long term safety of thepatient. Also, a lower airway pressure requires less energy consumptionand a less complex and therefore less expensive apparatus, which is alsogenerally quieter.

Low airway pressures are also desirable before and during the earlystage of each sleep period as the increased comfort of an initiallylower airway pressure allows the patient to more easily fall asleep.When a patient undergoing CPAP opens their mouth with pressurized airbeing forced through the nose, the pressured air exits out of the mouthproducing an unpleasant sensation. This can occur when the patient putson the mask connected to the pressured air supply before falling asleepand some patients will therefore leave the mask off for as long aspossible and may in fact fall asleep without wearing the mask andtherefore without the benefits of the CPAP therapy.

In addition to the problems associated with administering CPAP therapythere exists the inconvenience and cost of diagnosis which may beundertaken by overnight observation at a sleep clinic or the like. Hencea simple means whereby a patient's apnea problem can be diagnosed athome without supervision is clearly desirable as well as a CPAP devicewhich will deliver a continuously minimum appropriate pressure forsubstantially the entire period of therapy.

Although diagnosis in a sleep clinic as outlined above is beneficial, ithas some deficiencies. A patient is likely not to sleep in a fullyrelaxed state in an unfamiliar environment and a single night isinsufficient to obtain a pressure setting that will be optimal in thelong run. Thus home therapy at the pressure setting arrived at in thisway is likely to be less than 100% effective on some occasions andhigher than necessary for a substantial portion of the time. The costand inconvenience of a sleep study in a hospital setting are to beavoided if possible.

A skilled physician can usually recognize the symptoms of sleep apneafrom questioning and examining a patient. Where no other indications arepresent there is very little risk in attempting nasal CPAP therapywithout further testing as the treatment is fail safe and non-invasive.However, a very useful intermediate step would be to analyze the patternof respiratory waveforms (e.g., pressure, flow or sound) over one ormore full nights of sleep. Interpretation of these patterns togetherwith questioning and examination will, in many cases, provide sufficientconfirmation of apnea to prescribe nasal CPAP therapy. If nasal CPAPeliminates the symptoms of day time sleepiness (as assessed by thepatient) and of apneic snoring patterns (as assessed by analysis ofrecorded respiratory sounds while on nasal CPAP), the treatment can becontinued. Further check-ups can be conducted at intervals recommendedby the physician.

In the most general form of a CPAP treatment device, the intermediatestep before the device attempts CPAP pressure increases is to analyzethe patterns of the respiratory parameters that can be obtained fromsensors, such as a pressure sensor or flow sensor. As those skilled inthe art will recognize, these parameters include, in addition toacoustic rate of breathing, inhaled/exhaled air volume andinhaled/exhaled air flow rate, and provide comprehensive information forthe physician to assess the patient's condition. This additionalinformation, for example, generated by a pressure transducer, isavailable at additional cost and complexity. Similar information relatedto airflow may be estimated from the speed of or current supplied to theblower of the apparatus that is supplying the pressure to the mask in asystem where pressure changes are generated by changing the speed of theblower. Examples of such an implementation are disclosed in commonlyowned U.S. Pat. Nos. 5,740,795, 6,332,463 and 6,237,593, the disclosuresof which are hereby incorporated by reference.

The measurement of other parameters would provide further information toassist diagnoses, and the acoustic and/or other respiratory recordingsdescribed above can readily be used in conjunction with other monitorssuch as ECG and/or pulse oximetry. Suitable monitors are available tomeasure both these parameters in the home. The correlation betweenreduced oxygen saturation and apnea is sufficiently well established toinfer oxygen desaturation from the confirmation of an apneic event.

One index determined from these parameters is the Apnea Hypopnea Index.The Apnea Hypopnea Index (“AHI”) is an indicator of severity of apatient's sleep disordered breathing. The AHI is determined by addingthe total number of apneas and hypopneas the patient experienced over aparticular time period, such as during a sleep clinic study. Variousforms of AHI index are known by those skilled in the art.

However, in automated devices, sophisticated sensors and associatedalgorithms for detecting SOB events and determining an appropriateresponse to the detected events add a level of complexity to the devicethat may increase the cost, potentially making them too expensive forsome patients. Thus there is a need for a device that can accuratelyadjust the therapeutic pressures in response to SOB events to alleviatethe events but utilizing minimum hardware and minimized methodology forcontrolling the hardware.

BRIEF SUMMARY OF THE INVENTION

It is an objective of the invention to provide a device that can detectSOB events and automatically and effectively determine an appropriatepressure response.

It is an objective of the invention to provide such a device thatminimizes the pressure treatment but assures the provision of a minimumlevel of support necessary to treat the patient.

It is still a further objective to provide such a device with minimalcomponents to ensure that it is inexpensive and cost-effective todevelop and manufacture.

The invention is a device for detecting SOB events and adjustingpressure to prevent such events on a session-by-session basis, such asnight by night, rather than on a breath-by-breath basis. In the device,in a first session while providing a level of treatment pressure, anindicator of severity of SOB events is detected. For example, in thefirst session the device detects and records a total number of apneasand hypopneas. Preferably, the detection of such events does not resultin a change to the treatment pressure during that session. In asubsequent session, the treatment pressure is adjusted based on what thedevice learned during the previous session. Thus, the historic SOB indexfrom the previous session is compared to a threshold in a currentsession and the treatment pressure is currently adjusted based on thehistoric index. In other words, pressure changes in subsequent sessionsmay increase or decrease depending on the nature of the historic SOBindicator. For example, if the prior night's AHI is greater than athreshold of 8, the pressure is automatically increased for use duringthe new session. If the pressure is less than 8, the pressure maydecrease or stay the same. In one embodiment, patterns in changes overseveral prior sessions, such as consecutive nights, are analyzed toautomatically determine a pressure setting in a current session. Forexample, if the AHI is 0 for two consecutive nights, the pressure may bereduced for or in the next night's treatment.

In the preferred embodiment of the invention, an AHI index is determinedfrom a flow signal which is preferably calculated from speed of theblower or current to the blower without use of a differential pressuretransducer type flow sensor. Similarly, it is preferred that no pressuresensor be used in the setting of the pressure in the mask. Such aconfiguration assists in meeting the objectives as previously described.Further aspects of the invention are described in more detail herein.

BRIEF DESCRIPTION OF THE DRAWINGS

To satisfy the recited objectives, a description of the invention isprovided with reference to appended drawings that depict typicalembodiments of the invention and are not intended to limit the scope ofthe invention, in which:

FIG. 1 depicts the structure of an embodiment of a pressure treatmentapparatus suitable for implementing the methods of the currentinvention;

FIG. 2 is a flow chart of steps in a methodology for the control of apressure treatment apparatus for making pressure adjustments during atreatment session based on apnea/hypopnea (AHI) indices taken from anearlier treatment session;

FIG. 3 is a more detailed flow chart of steps in a methodology for thecontrol of a pressure treatment apparatus to determine an AHI during atreatment session; and

FIG. 4 is a more detailed flow chart of steps in a methodology for thecontrol of the adjustment of pressure treatment in a subsequent sessionbased upon an AHI taken during a prior treatment session.

DETAILED DESCRIPTION

In reference to FIG. 1, mask flow is measured using a flow sensor 4 fand/or pressure sensor 4 p with a pneumotachograph and differentialpressure transducer or similar device. A flow signal F(t) is derived andmask pressure is measured at a pressure tap using a pressure transducerto derive a pressure signal Pmask(t). The pressure sensor 4 p and flowsensor 4 f have only been shown symbolically in FIG. 1 since thoseskilled in the art would understand how to measure flow and pressure.Flow F(t) and pressure Pmask(t) signals are sent to a controller ormicroprocessor 6 which then determines how to adjust the blower.Alternatively, it is preferred that a flow signal f(t) and pressuresignal Pmask(t) be estimated or calculated in relation to the blowermotor by monitoring power supplied to the motor and/or the speed of themotor as disclosed in U.S. Pat. Nos. 5,740,795, 6,332,463 or 6,237,593,without the provision of flow and pressure sensors as described above.

The controller 6 is configured and adapted to implement the methodologydescribed in more detail herein and may include integrated chips, amemory and/or other instruction or data storage medium. For example,programmed instructions with the control methodology may be coded onintegrated chips in the memory of the device (e.g., firmware) or loadedas software.

The pressure delivery device includes a blower 8, which preferably is animpellor. The impellor 8 is controlled by a servo 10, receives ambientair through an inlet 12 and delivers pressurized air through an outlet14 defined by an air delivery conduit 16 and a mask 18 with anintegrated exhaust vent 20. The impellor, motor, and controller assemblydefine a blower assembly and are located within the blower housing 22.Various switches 24 and displays 26 are provided in the blower housing.A number of sensors are provided within the blower to monitor, amongother things, snore 28, motor speed 30, and motor current 32. Variousdevices known in the art can serve as these types of sensors. Acommunication interface 34 allows data to be transferred between theapparatus and an external device, such as a computer or controller.

Preferably, the device delivers a generally constant therapeutic levelof continuous positive airway pressure (CPAP) during any given treatmentsession. However, consistent with the control principles of theinvention as described herein, other types of pressure treatment may beimplemented in the apparatus, such as bi-level CPAP treatment or othervariants of natural patient-synchronized pressure changes.

A. Control of Pressure Adjustments Based on Historic AHI Determinations

As illustrated in FIG. 2, the pressure treatment apparatus implementscontrol based on historic AHI determinations. As shown in step 20,airway pressure treatment is provided to the patient during a firsttreatment session. In such a session, in the absence of historic AHI,the pressure treatment level will be set to a default low or minimumlevel, or a level prescribed by a physician or clinician. Preferably, noadjustments to the treatment pressure are made to change the level oftherapy in response to a current detection of an SOB event during thecurrent session. During the treatment session, in step 22, sleepdisordered breathing events are detected and an index of these events isdetermined. Preferably, apnea and hypopnea events are detected and anAHI, the AHI being initialized for the current session, is incrementedby the number of such detected events. In step 24, a new or subsequenttreatment session is initiated with the apparatus. In this subsequentsession, a therapeutic level of the treatment is set automatically as afunction of the SOB event related index that was determined in the priortreatment session.

In the preferred embodiment of the invention, each of the previouslydescribed treatment sessions is a different night's treatment with thedevice. Thus, an AHI may be recorded during use of the treatmentapparatus during a single night and saved at the conclusion of thesession. This saved AHI may then be utilized to set the treatmentpressure in the next use of the device, such as during the next night.To distinguish such sessions, the device may be configured to store theAHI on power down. Then it will utilize a previously recorded AHI, if itexists, in setting the treatment pressure after the device is powered onbut before or as treatment is commenced. Alternatively, other schemesfor ensuring the use of an AHI from a previously recorded session may beimplemented. In one alternative scheme, date and/or time of everydetermined AHI from all sessions are recorded and stored. During asubsequent use, checking is performed for the most recent AHI.Similarly, this may be implemented by checking the date of an AHIagainst an internal clock to permit the use of a previous day's AHI insetting treatment pressure.

While additional pressure treatment adjustments may be made in a currentsession based on a current AHI determination or on detection of an SOBrelated event, it is preferred that no such adjustments be made until asubsequent session. Similarly, the ramping of pressure from a lowpressure up to the set therapeutic treatment pressure such that thepatient can fall asleep before reaching the therapeutic level may alsobe implemented by the device.

B. Determination of an Apnea Hypopnea Index (AHI) in a First Session

As previously noted, the pressure treatment device preferably detectssleep disordered breathing events including apneas and hypopneas, bydetermining an Apnea-Hypopnea Index. Optionally, other SOB relatedindices may be used, for example, an apnea index, a hypopnea index orsome other SOB related index. The preferred determination methodology isillustrated in the flow chart of FIG. 3. At the beginning of a treatmentsession with the device, a current SOB index or AHI is reset orinitialized in step 30. During the delivery of pressure treatment, flowis continuously measured or determined in step 32. With flow informationor the flow signal (e.g., from a differential pressure transducer orderived from blower speed or power to the blower motor), measures ofventilation (e.g., an average flow determined over a period of time) arecalculated in a step 34.

Preferably, these ventilation measures include a short term measure anda long term measure. In one embodiment, a suitable recent ventilationmeasure or a short term average may be a low pass filtered flow signalutilizing a low pass filter having a time constant which is short withrespect to the duration of a breath, e.g., about 2 to 8 seconds. Asuitable longer term ventilation or longer term average measure of flowmay be a low pass filtered flow signal utilizing a low pass filterhaving a time constant which is long with respect to the duration of abreath, e.g., about 110 seconds.

These ventilation measures, including a short term measure and a longterm measure, are for purposes of comparing a more recent averagemeasure with a longer term average. From the results of such acomparison, either apneas or hypopneas may be detected in steps 36Aand/or 36B respectively. For example, in detecting a hypopnea, if theshort term average measure falls below the longer term average such thatit is less than 50% of the longer term average, a hypopnea may betallied or detected. Similarly, if the short term average falls belowthe longer term average such that it is less than 20% of the longer termaverage, an apnea may be tallied or detected.

In one embodiment of the invention an AHI scoring scheme may beimplemented as follows:

-   -   i. An apnea is scored if a 2 second moving average ventilation        drops below 25% of a recent average ventilation (time        constant=100s) for at least 10 consecutive seconds,    -   ii. A hypopnea is scored if an 8 second moving average drops        below 50% but not more than 25% of the recent average        ventilation for 10 consecutive seconds.

Those skilled in the art will recognize other methods or modificationsfor detecting hypopneas or apneas and determining an AHI or an SOB indexwhich will otherwise indicate severity in the patient's SOB symptoms.

After detecting either an apnea or a hypopnea event, an AHI may beincremented in step 37. After incrementing the AHI, the systemdetermines whether the session has ended at step 38. At this point, thesystem terminates at step 39. If the session is ongoing, the systemcycles back to step 32 to continue detecting apnea and hypopnea eventsand incrementing the AHI.

The total of these detected apneas and hypopneas for any given sessionwould make up the AHI used in the adjustment of treatment pressure in asubsequent session. Preferably, the AHI is determined by adding thetotal number of apneas and hypopneas the patient experienced over atreatment period covering a single night. Optionally, the AHI may be afunction of time such as an average hourly AHI determined over the totaltime for any given treatment session with the device such as a period ofsleep or a single night of sleep.

C. Adjustment of Treatment Pressure in Response to AHI in a SubsequentSession

As previously noted, preferably automated adjustments to the therapeuticlevel of the treatment pressure are only made or only take effect fortreatment in a subsequent session or subsequent night of treatment basedon an AHI determined in a prior session or previous night of treatment.That is, the automated dynamic pressure changes are on a night-by-nightbasis rather than a breath-by-breath basis. Thus, the device implementsan algorithm for adjusting the treatment pressure in a subsequentsession. For example, as illustrated in FIG. 4, after starting a new orentering a treatment session in step 40, the device may then evaluate apreviously recorded AHI in an evaluation step 42. Based on the detectedAHI from a prior session a new treatment pressure will be set.Optionally, for a first use or first session, the AHI may have a defaultof 0 such that no changes to the treatment pressure will be implementedin the first session. Similarly, a default pressure setting for thefirst use may be a low non-therapeutic value (e.g., about 1-3 cmH₂O) orsome other physician or clinician set value in a therapeutic range ofabout 4-20 cmH₂O.

In evaluating the historic AHI in step 42, if a prior session results inno detected apneas or hypopneas or only a few (e.g., AHI=0 or less than8), no pressure changes will be implemented and the treatment pressuresetting will remain from the prior session. Alternatively, for purposesof determining the minimum pressure necessary to prevent SOB, for an AHIof 0 or an AHI of less than 8 from the prior session, the device maylower the pressure in the new session. In lowering the pressure, thedevice may decrement the pressure by a fixed amount, (e.g., 0.25 cmH₂O)which is preferably lower than the pressure increase although they maybe the same. Thus, in setting the treatment pressure in step 44, the newpressure for the current setting will be the pressure from the priorsession less the fixed decrement amount.

However, if the AHI from the prior session is greater than 0 or greaterthan some low non-adjustment range (e.g., 1-8 events), the treatmentpressure will automatically increment upwards since such an AHI score isan indication of the need for an increase in treatment. Thus, based onthe high AHI from the previous night, the treatment pressure can beincreased by some increment. The treatment pressure increase isperformed with the intent to decrease the AHI towards a clinicallydesirable level in the subsequent night. The ideal treatment pressurewill decrease the AHI to a clinically desirable level but not be so farin excess of the minimum required pressure that it induces unnecessarydiscomfort. Therefore, the quantum of the incremental pressure increasemay vary depending upon the perceived clinical severity of the AHI. Forexample, the choice of incremental pressure increase may reflect theclinical observation that a relatively small increment will induce aclinically significant change where the patient has a relatively low AHI(e.g., a pressure increment of 0.5 cmH₂O for an AHI in the range of5-19) while a relatively larger increment will be appropriate to inducea clinically significant change where the patient has a relatively highAHI (e.g., a pressure increment of 2 cmH₂O for an AHI of 40 or higher).

Referring to FIG. 4, in the treatment pressure setting step 44, thetreatment pressure is automatically set for the new session to be theprevious session's pressure setting plus the increment. The treatmentpressure will then be delivered during the current session in step 46and then, at step 48, the system cycles back to step 30 (FIG. 3) andagain begins the process of determining a new AHI. The new AHI willaffect the treatment pressure for the next session or treatment in thenext night or future session. Such a scheme allows the device to adjustitself over an unlimited number of nights, while evolving with the needsof the patient.

In one embodiment, other schemes of adjustment of the pressure may bebased on patterns of the AHI over more than a single night, such as twoor more nights. For example, the pressure may be lowered if the AHI hasbeen 0 for two or more consecutive sessions. Similarly, pressure may beincreased only if the AHI in more than one consecutive night, forexample, 2 or 3 nights, suggests a need for an increase. Preferably, anydecay in pressure over time is slower than the increase in pressure overtime.

Optionally, the device may be configured with an adaptation range thatlimits the changes to the treatment pressure that the device mayautomatically implement based on a previous night's AHI determination.The adaptation range may be a preset variable that is determined by aphysician and preferably is not changed during the many treatmentsessions with the user or patient. A default range may be set into thedevice in the absence of such a setting by a physician. For example, thephysician may preset the adaptation range to a value of 10 cmH₂O. When apressure change is implemented by the device, the range is checked tomake certain that any increments attempted by the device never exceedthe original pressure setting of the physician by the amount of therange. Thus, if the pressure is set to 5 cmH₂O for the first sessionwith a patient, and the adaptation range is set to 10 cmH₂O, anyautomated treatment pressure change that attempts to increment thetreatment pressure beyond 15 cmH₂O would be prevented. In addition, thedevice may be configured with an optional warning indicator to advisethe patient or the physician of the attempted increase beyond theadaptation range.

A device that implements the above-described treatment scheme would havemany benefits for SOB patients. For example, utilizing the describedalgorithm would be more cost effective when compared to more complexdetection and adjustment schemes. Also, since the device can adjust on anight-by-night basis, it can provide adaptation for seasonal changesthat may affect the patient's condition. It can also adapt with thepatient's disease progression.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not as restrictive. The scope of the invention is, therefore,indicated by the appended claims and their combination in whole or inpart rather than by the foregoing description. All changes that comewithin the meaning and range of equivalency of the claims are to beembraced within their scope.

1. An apparatus for providing positive airway pressure, comprising: ablower configured to provide pressurized air to a patient interface; acontroller configured to: control an air pressure provided by the blowerat a first therapeutic pressure treatment level during a first treatmentsession; detect the occurrence of sleep disordered breathing (SDB)events during the first treatment session; and adjust the firsttherapeutic pressure treatment level in response to the detected SDBevents during the first treatment session; in a setting procedure,determine a second generally constant therapeutic pressure treatmentlevel to be provided in a second treatment session, the second treatmentsession being subsequent to the first treatment session, the secondgenerally constant therapeutic pressure treatment level being determinedbased on checking of a clock and the sleep disordered breathing (SDB)events detected from the first treatment session; and maintain the airpressure at the second generally constant therapeutic pressure treatmentlevel without changing the therapeutic pressure treatment level duringthe second treatment session, wherein the first treatment sessioncomprises at least one sleep session and the second treatment sessioncomprises a different sleep session.
 2. The apparatus of claim 1,wherein the controller is configured to detect the occurrence of sleepdisordered breathing (SDB) events during the second treatment session.3. The apparatus of claim 1, wherein the first treatment session is aninitial treatment session.
 4. The apparatus of claim 1, wherein in athird treatment session, the third treatment session being subsequent tothe second treatment session, the setting procedure is repeated usingthe sleep disordered breathing (SDB) events detected from the secondtreatment session to determine a third generally constant therapeuticpressure treatment level for use in the third treatment session.
 5. Theapparatus of claim 1, wherein the setting procedure is repeatedperiodically for further subsequent treatment sessions.
 6. The apparatusof claim 1, wherein the setting procedure is repeated on a nightly basisusing the SDB events detected from a previous treatment session.
 7. Theapparatus of claim 5, wherein the periodic repeat of the settingprocedure occurs before each treatment session.
 8. The apparatus ofclaim 1, wherein the SDB events include apnea and hypopnea events. 9.The apparatus of claim 4, wherein the second and third treatmentsessions are successive sessions.
 10. The apparatus of claim 4, whereinthe controller determines a generally constant therapeutic pressuretreatment level by comparing a total number of the SDB events detectedfrom a previous treatment session with a threshold.
 11. The apparatus ofclaim 10, wherein the third generally constant therapeutic pressuretreatment level is identical to the second generally constanttherapeutic pressure treatment level, when the total number of thedetected SDB events is less than the threshold.
 12. The apparatus ofclaim 10, wherein the third generally constant therapeutic pressuretreatment level is less than the second generally constant therapeuticpressure treatment level, when the total number of the detected SDBevents is less than the threshold.
 13. The apparatus of claim 10,wherein the third generally constant therapeutic pressure treatmentlevel is greater than the second generally constant therapeutic pressuretreatment level, when the total number of the detected SDB events isequal to or greater than the threshold.
 14. The apparatus of claim 1,wherein the controller is further configured to store the detected SDBevents.
 15. The apparatus of claim 1, wherein the controller isconfigured to access an index of the detected SDB events from a previoustreatment session by checking the date of the index of the detected SDBevents in relation to the clock.
 16. A method for controlling anapparatus that provides positive airway pressure, comprising:controlling with a processor setting of a blower for an air pressureprovided at a first therapeutic pressure treatment level during a firsttreatment session, the blower configured to provide pressurized air to apatient interface; detecting with the processor the occurrence of sleepdisordered breathing (SDB) events during the first treatment session;and adjusting with the processor the first therapeutic pressuretreatment level in response to the detected SDB events during the firsttreatment session; in a setting procedure, determining with theprocessor a second generally constant therapeutic pressure treatmentlevel to be provided in a second treatment session, the second treatmentsession being subsequent to the first treatment session, the secondgenerally constant therapeutic pressure treatment level being determinedbased on checking of a clock and the sleep disordered breathing (SDB)events detected from the first treatment session; and maintaining withthe processor control of the air pressure of the blower at the secondgenerally constant therapeutic pressure treatment level without changingthe therapeutic pressure treatment level during the second treatmentsession, wherein the first treatment session comprises at least onesleep session and the second treatment session comprises a differentsleep session.
 17. The method of claim 16, wherein the detectingcomprises detecting the occurrence of sleep disordered breathing (SDB)events during the second treatment session.
 18. The method of claim 16,wherein the first treatment session is an initial treatment session. 19.The method of claim 16, wherein for a third treatment session controlledby the processor, the third treatment session being subsequent to thesecond treatment session, the setting procedure is repeated by theprocessor using the sleep disordered breathing (SDB) events detectedfrom the second treatment session to determine a third generallyconstant therapeutic pressure treatment level for use in the thirdtreatment session.
 20. The method of claim 16, wherein the processorperiodically repeats the setting procedure for further subsequenttreatment sessions.
 21. The method of claim 16, wherein the processorrepeats the setting procedure on a nightly basis using the SDB eventsdetected from a previous treatment session.
 22. The method of claim 21,wherein the periodic repeat of the setting procedure occurs before eachtreatment session.
 23. The method of claim 16, wherein the SDB eventsinclude apnea and hypopnea events.
 24. The method of claim 19, whereinthe second and third treatment sessions are successive sessions.
 25. Themethod of claim 19, wherein the processor determines a generallyconstant therapeutic pressure treatment level by comparing a totalnumber of the SDB events detected from a previous treatment session witha threshold.
 26. The method of claim 25, wherein the third generallyconstant therapeutic pressure treatment level is identical to the secondgenerally constant therapeutic pressure treatment level, when the totalnumber of the detected SDB events is less than the threshold.
 27. Themethod of claims 25, wherein the third generally constant therapeuticpressure treatment level is less than the second generally constanttherapeutic pressure treatment level, when the total number of thedetected SDB events is less than the threshold.
 28. The method of claims25, wherein the third generally constant therapeutic pressure treatmentlevel is greater than the second generally constant therapeutic pressuretreatment level, when the total number of the detected SDB events isequal to or greater than the threshold.
 29. The method of claim 16,wherein the processor stores the detected SDB events.
 30. The method ofclaim 16, wherein the processor accesses an index of the detected SDBevents from a previous treatment session by checking the date of theindex of the detected SDB events in relation to the clock.